The degree to which non-adrenergic vascular resistance increases operate in conditions of external circulatory support is unknown. Although increased venous content of norepinephrine is well recognized from organs with adrenergically innervated vasculature, e.g. spleen and kidney, no actual secretion rates of norepinephrine have been described from these or other peripheral locations. In addition, no direct correlations have been made between peripheral norepinephrine release and increased resistance to blood flow. Norepinephrine content of splenic venous, left renal venous and arterial blood will be determined simultaneously with splenic arterial and left renal arterial flow measured electromagnetically. Gradients between arterial and venous pressure across the left kidney and spleen will be monitored. The data will permit calculation of true norepinephrine secretion rates from spleen and left kidney and calculation of simulataneous vascular resistance in the same two organs. Norepinephrine will be analyzed by a trihydroxyindole technique. Resting conditions and acutely denervated preparations will be evaluated first. Reflex responsiveness of norepinephrine release and vascular resistance to acute hypovolemia will then be studied. Next, reflex norepinephrine release and vascular resistance patterns will be studied in response to graded changes in pulse amplitude and mean carotid sinus pressure reaching isolated, bilateral, innervated carotid sinus loops from an external pump circuit under independent control. Finally, the same pulse parameter changes will be directly introduced to the splenic and left renal circulation to determine any local effects pulse parameters exert on vascular resistance and norepinephrine release. Data from comparable experiments will be grouped and statistically evaluated by analysis of variance using Students T-test. Where it is appropriate to the evaluation of graded pulse parameter changes, regression analysis will be carried out and significance levels derived from the associated correlation co-efficients.